1. Field of the Invention
The present invention relates to a lever operated hoist in a structure designed not to lift the load if a load heavier than a preset rated load is suspended, and more particularly to a lever operated hoist capable of adjusting the position of the lower hook in the heightwise direction under load without disconnecting the coupling of the pinion of the drive shaft and the load sheave.
2. Description of the Prior Art
In a lever operated hoist in an unloaded state, hitherto, to adjust the position by moving the lower hook in the heightwise direction by pulling the load chain fitted to the load sheave, one of the following methods was employed.
1. By moving the drive shaft to the operating wheel side, the coupling of the pinion fixed at one end of the drive shaft and the gear train for transmitting rotation to the load sheave is canceled to set the load sheave free to rotate, and the load chain is pulled in this free state.
2. By moving the pressing drive member to the operating wheel side and pulling apart from the pressure bearing member to set the load sheave free to rotate, the load chain is pulled in this free state.
These methods, however, involved the following problems, and their improvements have been desired.
(1) That is, in the first method, the load sheave cleared of coupling with the drive shaft side is braked by a small force in free state.
Therefore, in the event of an incidental disconnection of the coupling of the drive shaft and load sheave during work, the load sheave is set in free state, and the load may drop unexpectedly, or the load may be loosened to lead to an accident.
Or when pulling the load chain to move the lower hook in the uncoupled state of the drive shaft and the load sheave, this moving speed may be faster than expected by the operator, and the operator may be exposed to an unexpected accident.
Still more, when lifting up the next load, or when setting down, it is additionally necessary to move the drive shaft once uncoupled from the load sheave side in free state to the gear train side while rotating, and adjust the pinion fixed at one end of the drive shaft to be engaged with the gear train.
(2) In the second method, when the lower hook is adjusted in position in the heightwise direction in an unloaded state, the rotation of the load sheave becomes heavy, and it is difficult to rotate continuously with a small action force.
Accordingly, every time the free rotation of the load sheave becomes heavy, it was necessary to manipulate the operation lever to loosen the pressing drive member repeatedly.
Incidentally, the present inventor closely investigated into the cause of the rotation of the load sheave becoming heavy, and discovered that the pressing drive member moved in the direction of departing from the pressure bearing member contacts with the outside cover of the operation lever or other constituent member to develop a contact friction force, thereby causing to impede the free rotation of the load sheave.